Adaptive selection of transmission parameters for reference signals

ABSTRACT

A method and apparatus for defining transmission parameters of user equipment reference signals. The method includes estimating channel delay spreads of a plurality of user equipments scheduled for transmission at a particular transmission time period or sub-frame in an uplink for communication with a NodeB, and allocating transmission parameters to each scheduled user equipment of the plurality of user equipments in accordance to the delay spreads of the plurality of user equipments scheduled for transmission in the particular time period or sub-frame, wherein the parameters comprises a cyclic shift allocated to each m-th user equipment equal to the sum of a delay spread and a timing uncertainty of each of the previous m-1 user equipments.

CLAIM OF PRIORITY

This application is a continuation to U.S. patent application Ser. No.11/839,421, filed on Aug. 15, 2007, which claims priority to U.S. PatentProvisional Application No. 60/823,211, filed Aug. 22, 2006, which areincorporated by reference herein.

FIELD OF THE INVENTION

Embodiments of this invention generally relate to wireless communicationand in particular to generation of reference signals sent by mobileusers.

BACKGROUND OF THE INVENTION

The Global System for Mobile Communications (GSM: originally from GroupeSpecial Mobile) is currently the most popular standard for mobile phonesin the world and is referred to as a 2G (second generation) system.Universal Mobile Telecommunications System (UMTS) is one of thethird-generation (3G) mobile phone technologies. Currently, the mostcommon form uses W-CDMA (Wideband Code Division Multiple Access) as theunderlying air interface. W-CDMA is the higher speed transmissionprotocol designed as a replacement for the aging 2G GSM networksdeployed worldwide. More technically, W-CDMA is a widebandspread-spectrum mobile air interface that utilizes the direct sequenceCode Division Multiple Access signaling method (or CDMA) to achievehigher speeds and support more users compared to the older TDMA (TimeDivision Multiple Access) signaling method of GSM networks.

Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-userversion of the popular Orthogonal Frequency-Division Multiplexing (OFDM)digital modulation scheme. Multiple access is achieved in OFDMA byassigning subsets of sub-carriers to individual users. This allowssimultaneous low data rate transmission from several users. Based onfeedback information about the channel conditions, adaptiveuser-to-sub-carrier assignment can be achieved. If the assignment isdone sufficiently fast, this further improves the OFDM robustness tofast fading and narrow-band co-channel interference, and makes itpossible to achieve even better system spectral efficiency. Differentnumber of sub-carriers can be assigned to different users, in view tosupport differentiated Quality of Service (QoS), i.e. to control thedata rate and error probability individually for each user. OFDMA isused in the mobility mode of IEEE 802.16 WirelessMAN Air Interfacestandard, commonly referred to as WiMAX. OFDMA is currently a workingassumption in 3GPP Long Term Evolution (LTE) downlink. Also, OFDMA isthe candidate access method for the IEEE 802.22 “Wireless Regional AreaNetworks”.

NodeB is a term used in UMTS to denote the BTS (base transceiverstation). In contrast with GSM base stations, NodeB uses WCDMA or OFDMAas air transport technology, depending on the type of network. As in allcellular systems, such as UMTS and GSM, NodeB contains radio frequencytransmitter(s) and the receiver(s) used to communicate directly with themobiles, which move freely around it. In this type of cellular networksthe mobiles cannot communicate directly with each other but have tocommunicate with the BTSs

Traditionally, the NodeBs have minimum functionality, and are controlledby an RNC (Radio Network Controller). However, this is changing with theemergence of High Speed Downlink Packet Access (HSDPA), where some logic(e.g. retransmission) is handled on the NodeB for lower response timesand in 3GPP LTE (a.k.a. E-UTRA) almost all the RNC functionalities havemoved to the NodeB.

The utilization of cellular technologies allows cells belonging to thesame or different NodeBs and even controlled by different RNC to overlapand still use the same frequency. The effect is utilized in softhandovers.

Since WCDMA and OFDMA often operates at higher frequencies than GSM, thecell range is considerably smaller compared to GSM cells, and, unlike inGSM, the cells' size is not constant (a phenomenon known as “cellbreathing”). This requires a larger number of NodeBs and carefulplanning in 3G (UMTS) networks. Power requirements on NodeBs and UE(user equipment) are much lower.

A NodeB can serve several cells, also called sectors, depending on theconfiguration and type of antenna. Common configuration include omnicell (360°), 3 sectors (3×120°) or 6 sectors (3 sectors 120° wideoverlapping with 3 sectors of different frequency).

High-Speed Packet Access (HSPA) is a collection of mobile telephonyprotocols that extend and improve the performance of existing UMTSprotocols. Two standards HSDPA and HSUPA have been established. HighSpeed Uplink Packet Access (HSUPA) is a packet-based data service ofUniversal Mobile Telecommunication Services (UMTS) with typical datatransmission capacity of a few megabits per second, thus enabling theuse of symmetric high-speed data services, such as video conferencing,between user equipment and a network infrastructure.

An uplink data transfer mechanism in the HSUPA is provided by physicalHSUPA channels, such as an Enhanced Dedicated Physical Data Channel(E-DPDCH), implemented on top of the uplink physical data channels suchas a Dedicated Physical Control Channel (DPCCH) and a Dedicated PhysicalData Channel (DPDCH), thus sharing radio resources, such as powerresources, with the uplink physical data channels. The sharing of theradio resources results in inflexibility in radio resource allocation tothe physical HSUPA channels and the physical data channels.

The signals from different users within the same cell may interfere withone another. This type of interference is known as the intra-cellinterference. In addition, the base station also receives theinterference from the users transmitting in neighboring cells. This isknown as the inter-cell interference

When an orthogonal multiple access scheme such as Single-CarrierFrequency Division Multiple Access (SC-FDMA)—which includes interleavedand localized Frequency Division Multiple Access (FDMA) or OrthogonalFrequency Division Multiple Access (OFDMA)—is used; intra-cellmulti-user interference is not present. This is the case for the nextgeneration UMTS enhanced-UTRA (E-UTRA) system—which employs SC-FDMA—aswell as IEEE 802.16e also known as Worldwide Interoperability forMicrowave Access (WiMAX)—which employs OFDMA. In this case, thefluctuation in the total interference only comes from inter-cellinterference and thermal noise which tends to be slower. While fastpower control can be utilized, it can be argued that its advantage isminimal.

In the uplink (UL) of OFDMA frequency division multiple access (bothclassic OFDMA and SC-FDMA) communication systems, it is beneficial toprovide orthogonal reference signals (RS), also known as pilot signals,to enable accurate channel estimation and channel quality indicator(CQI) estimation enabling UL channel dependent scheduling, and to enablepossible additional features which require channel sounding.

Channel dependent scheduling is widely known to improve throughput andspectral efficiency in a network by having the Node B, also referred toas base station, assign an appropriate modulation and coding scheme forcommunications from and to a user equipment (UE), also referred to asmobile, depending on channel conditions such as the receivedsignal-to-interference and noise ratio (SINR). In addition to channeldependent time domain scheduling, channel dependent frequency domainscheduling has been shown to provide substantial gains over purelydistributed or randomly localized (frequency hopped) scheduling inOFDMA-based systems. To enable channel dependent scheduling, acorresponding CQI measurement should be provided over the bandwidth ofinterest. This CQI measurement may also be used for link adaptation,interference co-ordination, handover, etc.

One method for forming reference signals is described in US patentapplication 20070171995, filed Jul. 26, 2007 and entitled “Method andApparatus for Increasing the Number of Orthogonal Signals Using BlockSpreading” and is incorporated by reference herein. The generation ofreference signals (RS) sequences can be based on the constant amplitudezero cyclic auto-correlation (CAZAC) sequences, and the use of blockspreading for multiplexing RS from multiple UE transmitters is describedtherein.

SUMMARY OF THE INVENTION

Embodiments of the present invention use dynamically estimated channeldelay spreads of mobile users, to assign parameters which definetransmissions of reference signals (RS). Exemplary embodiments determinea set of allocated cyclic shift values that are tailored to the channeldelay spreads. The set of allocated cyclic shift values are used by acorresponding set of user equipment (UE) being served by a NodeB to formreference signals. Each UE uses the allocated cyclic shift to form itsreference signal by applying the cyclic shift to a reference sequence.In some embodiments, the reference sequence is a modulatedConstant-Amplitude-Zero-Auto Correlation (CAZAC) sequence. The set ofallocated cyclic shift values can be updated periodically to compensatefor changes in UEs delay spreads.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is a representation of two cells in a cellular communicationnetwork that includes an embodiment of adaptive cyclic shifting ofreferences signals;

FIGS. 2A and 2B show two exemplary sub-frame structures that includereference signals according to an embodiment of the present invention;

FIG. 3 is a block diagram of an SC-FDMA system for transmitting thesub-frame structures of FIG. 1;

FIGS. 4A and 4B illustrate alternative embodiments of sub-carriermapping in the system of FIG. 3;

FIG. 5 illustrates exemplary delay spread plots and correspondingadaptive cyclic shift selections for a representative pool of mobiledevices;

FIG. 6 illustrates adaptive cyclic shift selections of reference signalsfor four representative mobile devices of FIG. 5 at a different point intime;

FIG. 7 is a flow chart illustrating adaptive allocation of cyclicshifts; and

FIG. 8 is a block diagram illustrating a mobile device that usesadaptive cyclic shift selection for reference signals.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a representation of two cells in a cellular communicationnetwork 100 that includes an embodiment of adaptive cyclic shifting ofreferences signals. In this representation only two cells 102-103 areillustrated for simplicity, but it should be understood that the networkincludes a large matrix of cells and each cell is generally completelysurrounded by neighboring cells. A representative set of user equipmentU1-U2 is currently in cell 102 and is being served by NodeB N1. Cell 103is a neighbor cell and NodeB N2 is not serving UE U1-U2. UE U1 and U2are representative of a set of user equipment in any given cell sincethere will typically be tens or hundreds of UE in each cell. Each UEcommunicates with its serving NodeB using an uplink transmission UL anda downlink transmission DL.

As mentioned above, in the uplink (UL) of frequency division multipleaccess (OFDMA, SC-FDMA, etc) communication systems, it is beneficial toprovide orthogonal reference signals (RS), also known as pilot signals,to enable accurate channel estimation and channel quality indicator(CQI) estimation enabling UL channel dependent scheduling.

FIGS. 2A and 2B show exemplary sub-frame structures 200A and 200B thatincludes reference signals, according to an embodiment of the presentinvention. Exemplary sub-frame structure 200A is one possible sub-framestructure used by a UE for UL transmissions in an OFDMA based system,such as a DFT (Discrete Fourier Transform) spread OFDMA system or aSC-FDMA system. Exemplary sub-frame structure 200B is another possiblesub-frame structure used for the same purpose.

Sub-frame 200A comprises of two short blocks (SBs) 202 and six longblocks (LBs) 204 and in the exemplary embodiment it is assumed to haveduration of 0.5 milliseconds (msec). All blocks are preceded by a cyclicprefix transmission 206 to protect the corresponding data against thechannel delay spread and the respective multi-path propagation. In theexemplary embodiment 200A, data (including control related ones) areassumed to be transmitted in the LBs while reference signals (RS), alsoreferred to as pilots, are assumed to be transmitted in the SBs.Combination of SBs into LBs for the RS transmission may be alternativelyapplied. The transmission time interval (TTI) of a UE may extend overone or several sub-frames. Sub-frame 200B shows another exemplaryembodiment of the 0.5 ms sub-frame structure. In the sub-frame 200B, theRS could be located in any of the symbols, such as for example LB #1,which is the first symbol, or LB #4, which is the middle symbol.

FIG. 3 presents a block diagram for a transmitter 300 in a SC-FDMAsystem. The information bits, after passing through the coding blocks302, including an encoder, a CRC attachment and an interleaver, areprovided to the modulating unit of the SC-FDMA system. After applying aDiscrete Fourier Transform (DFT) 308 on the data, which may also be anACK/NAK or a CQI related to the downlink (DL) communication, mapping 310of the DFT output is performed on a selected part of the operatingbandwidth (BW). This mapping may be localized, implying that the datasub-carriers occupy a continuous part of the BW, or distributed,implying that the data sub-carriers occupy a discontinuous part of theBW. Subsequently, an Inverse Fast Fourier Transform (IFFT) 312 operationis applied, followed by CP insertion 314, time windowing 316 to producea signal with the desired spectral characteristics, a digital-to-analogconverter (DAC) 318, and finally the transmission (Tx) radio frequency(RF) circuitry 320 which includes a power amplifier and the transmitterantenna. In addition the UE may be responsive to Node B signalingindicating a transmit time and/or transmit power adjustment. Similarprocessing can be applied for the RS which is not modulated signal(carries no information) in order to allow the Node B to perform channelrelated estimation functions. The RS can be generated from a CAZAC-basedsequence 304 and is subsequently cyclically shifted 306 prior to beingsent to the DFT 308 for the same functions as for the data transmissionto occur thereafter. As the DFT of a predetermined RS-sequence (whichcan be CAZAC-based sequence) is known in advance, this operation may beomitted, and sub-carrier mapping 310 of the frequency domainrepresentation of the RS-sequence can be performed with the cyclic shiftapplied after the IFFT 312. This alternate embodiment, where cyclicshift is applied after the IFFT, is shown in FIG. 5.

FIGS. 4A and 4B illustrate alternative embodiments of sub-carriermapping in the system of FIG. 3. In FIG. 4A, the mapping 310A islocalized as illustrated by the data sub-carriers occupying a continuouspart of the BW with zero padding elsewhere. In FIG. 4B the mapping 310Bis distributed as illustrated by the data sub-carriers occupying adiscontinuous part of the BW with zeros inserted on interveningsub-carrier slots.

Mapping unit 310 produces localized and distributed transmissions in thefrequency domain. Control module 311 is responsive to schedulingcommands received on the downlink from the serving NodeB and configuresmapping unit 310 in response to the received commands. Morespecifically, the scheduling operation refers to localized signaltransmission in contiguous parts of bandwidth (BW), referred to asresource blocks (RBs). In the some embodiments, the RBs assigned to a UEare consecutive, but in general they may be anywhere in the overallscheduling BW. The scheduling BW during a given time period is typicallyonly a part of the total operating BW.

In order for the Node B to obtain a CQI estimate for the UL channel of aUE over the scheduling BW, and thereby perform frequency and/or timedomain channel dependent scheduling, the UE needs to transmit a RS overthe scheduling BW or over the entire BW (distributed RS). On the otherhand, in order to minimize losses from channel estimation, a UE needs totransmit a RS only over the RBs where the UE transmission is scheduled(localized RS) in order to avoid unnecessarily dispersing its transmitpower over a wider bandwidth. For this reason, a UE typically transmitsa RS, other than the RS associated with data demodulation (DM RS), overa relatively wide bandwidth to enable its serving Node B to obtain a CQIestimate and perform time and/or frequency domain scheduling for the UEover that bandwidth. This RS effectively provides channel sounding overits transmission bandwidth and is referred to as sounding RS (SRS) orCQI RS. As it is typically not the same as the DM RS, it is transmittedduring a different a symbol replacing data transmission.

In general, there are two significant limitations in the UL that makefrequency dependent scheduling more difficult than in the DL. First, theUEs are transmit power limited which makes accurate CQI estimationchallenging, particularly for UEs located near the geographic boundaryof the cell and/or whose signals are received at the Node B with lowsignal-to-interference and noise ratio (SINR). Also, unlike the DL wherethe CQI estimate may be averaged over several sub-frames, as a RS istransmitted in all sub-frames, in the UL this is only possible if a UEtransmits a SRS during consecutive sub-frames, which would result in anunacceptable increase in UL overhead. The overhead associated with thetransmission SRSs should be less the resulting scheduling gains in ULthroughput. Second, each of multiple UEs devices needs to transmit aseparate SRS for CQI measurements, making the efficient multiplexing ofsuch reference signals an important issue.

In the past, the transmission of UE reference signals (RS) is specifiedindependently of a UE's dynamically estimated delay spread. The drawbackof such solution is that the reference signal parameters are nottailored to a users dynamically changing delay spreads, and thus, theresources which are assigned to reference signals aren't efficientlyutilized. As a result, the selected cyclic shift used by all UEs istypically larger than needed. The consequence of using a large cyclicshift for all UEs is that there are fewer RS sequences (different cyclicshifts thereof) available for allocation to UEs.

In contrast to prior art, embodiments of the present inventiondynamically allocates transmission parameters of reference signals,depending on measurements of UEs delay spreads. In exemplaryembodiments, the transmission parameters of reference signals are cyclicshifts of reference sequences. Reference sequences can be generated bymodifying and modulating CAZAC sequences, which are sequences with goodcorrelation properties.

One construction method for uplink (UL) RS among UEs belonging in agiven pool of multiplexed UEs having RS transmission over the samebandwidth, is for each UE to transmit a RS formed by cyclic shift of aConstant-Amplitude-Zero-Auto-Correlation (CAZAC) sequence, such as aZadoff-Chu sequence. Multiplexed UEs use distinct integer multiples ofthe same baseline cyclic shift. It is important to note that as the NUEs from the given pool use a common pool of sub-carriers, the onlydistinction between their RS transmissions is the value of the CyclicShift. Thus, the resulting RS signals are said to be orthogonal in thecode domain (CDM of the RS). Different cells may use different baseCAZAC sequences.

To facilitate the understanding of the invention, FIG. 5 illustratesexemplary delay-spread plots and corresponding adaptive cyclic shiftselections for a representative pool of eight mobile devices. FIG. 5exemplifies a use of the method for adaptively specifying the cyclicshift size allocated for orthogonal RS generation at each UE dependingon the channel delay spread and the timing error which is experienced byeach of the simultaneously multiplexed UEs.

In typical deployment instances, UEs whose signals experience largedelay spreads will be multiplexed with UEs whose signals experience lowdelay spreads. In such scenarios, cyclic shifts to scheduled UEs for theformation of orthogonal RS can be allocated adaptively, in accordance tothe delay spreads of scheduled UEs. The cyclic shift value may also beadapted to the operating environment so that a small cyclic shift valueis used in channels with small signal delay spreads, such as channelsencountered in indoor environments, while a large cyclic shift value isused otherwise (outdoor environments). Throughout this document,reference to “a scheduled UE during a given time instance” means any UEhaving an UL signal transmission whether it is just an RS transmissionor it includes additional data signals.

For a constant cyclic shift value, a multiple of which being applied toa corresponding multiple of UEs having RS transmission in the samebandwidth, the number of available cyclic shifts equal to themathematical floor of the ratio of the symbol duration divided by thecyclic shift duration. Therefore, for symbol duration of 33 μsec andcyclic shift duration of 5 μsec, there are a total of 6 available cyclicshifts and the RS from 6 UEs can be orthogonally multiplexed throughdifferent cyclic shifts. With adaptive cyclic shift allocation accordingto the delay spread experienced by each UE, the multiplexing capacitycan be increased as more cyclic shifts become available. FIG. 5describes an example of the proposed adaptive cyclic shift allocation,where 8 orthogonal RS and corresponding UEs are simultaneously supportedeven though the worst—case delay spread is 5 μsec.

In the embodiment represented by FIG. 5, the time length of a shortblock is 33 μsec, referring back to SB1 202 of FIG. 2. A CAZAC length isselected to require the same amount of time for transmission. At onegiven point in time, UE-1 has an estimated delay spread and timinguncertainty 501 of 2 μsec. Similarly, UE-2 has an estimated delay spreadand timing uncertainty 501 of 3 μsec, UE-7 has an estimated delay spreadand timing uncertainty 507 of 5 μsec, and UE-8 has an estimated delayspread and timing uncertainty 507 of 4 μsec, for example.

In general, if a total of M UEs are to be multiplexed, the cyclic shiftallocated to the m-th UE is equal to the sum of the largest (estimated)timing uncertainties and delay spreads of previous m-1 UEs. Thus, UE-1is allocated the original sequence with no cyclic shifts 511. UE-2 isallocated a cyclic shift 512 which equals the timing uncertainty+delayspread of the first UE, which is 2 μsec, etc. UE-7 is allocated a cyclicshift 517 which equals to the timing uncertainty+delay spread of thefirst six UEs, and UE-8 is allocated a cyclic shift 518 which equals tothe timing uncertainty+delay spread of the first seven UEs. Note thatthe original sequence length equals the RS duration. For example, if thesequence length is 151 and the RS duration is 33.3 μsec, then the cyclicshift of 1 μsec roughly corresponds to the cyclic shift of ceil(151/33.3)=5 samples. In general, if the sequence length is L and the RSduration is τ μsec, then a cyclic shift of τ₀ μsec means a cyclic shiftof the sequence by ceil (L*τ₀/τ) samples, where “ceil” denotes themathematical ceiling operation. Other cyclic shifts which areapproximately close to ceil (L*τ₀/τ) are not precluded [for exampleround (L*τ₀/τ)], where “round” denotes the mathematical roundingoperation of a real number to its closest integer. Thus, given a mixtureof UEs with high and low delay spreads, the number of supportable UEswith orthogonal RS increases substantially. Table 1 gives a completeexample for the representative pool of FIG. 5.

TABLE 1 example allocated shifts at one point in time Timinguncertainty + delay spread Allocated cyclic shift UE-1 2 μsec 0 μsecUE-2 3 μsec 2 μsec UE-3 4 μsec 5 μsec UE-4 5 μsec 9 μsec UE-5 5 μsec 14μsec UE-6 5 μsec 19 μsec UE-7 5 μsec 24 μsec UE-8 4 μsec 29 μsec

In this example, if all of the UEs were allocated the same cyclic shiftbased on a worst case timing uncertainty and delay spread time of 5μsec, then only six UEs could be included in the pool instead of eight.The same concept can be extended for the case the cyclic shift isadapted to the operating environment where even though a multiple of abase cyclic shift value may be used by a UE, the base cyclic shift valueis selected according to the operating environment and is not always thelargest one corresponding to the worst operating conditions.

FIG. 6 illustrates adaptive cyclic shift selections of reference signalsfor representative mobile devices of FIG. 5 at a different point intime. Thus, in this embodiment, the allocated cyclic shift is updatedperiodically. As UEs move around in the cell differences in transmissiondistance and obstacles will cause the delay spread of each UE to change.Some delay spread will get longer and some will get shorter. Forexample, in FIG. 6, UE-1 now has a delay spread of 5 μsec which causesan allocated cyclic shift 602-603 in UE-2 to be 5 μsec. UE-2 now has adelay spread of 2 μsec which causes an allocated cyclic shift 604-605 inUE-3 to be 7 μsec, etc. Typically, the sum will always be less than ifthe worst case amount was assumed for all, therefore more UEs can besupported in each cell.

Some downlink (DL) control signaling will be required to specify thecyclic shift for each UE that is selected based on the actual UE need(delay spread and timing uncertainty) and not always set at a maximumvalue to support a worst case scenario. The number of bits required toindicate the allocated cyclic shift is very small assuming somequantization of the smallest possible cyclic shift corresponding to alowest delay spread channel and timing uncertainty and larger cyclicshifts being defined relative to the lowest one. Moreover, the cyclicshift value allocated to each UE varies much slower than the sub-frameor TTI duration, assumed to be in the order of 1 msec, as the delayspread and timing error remain constant over a much longer period. Forexample, the delay estimation for each UE may be updated at about thesame rate as its transmission timing which is in the order of hundredsof milliseconds or even in the order of seconds.

FIG. 7 is a flow chart illustrating adaptive allocation of cyclicshifts. As described above, an estimate 702 is made by the serving NodeBof the delay spread for each UE in a pool that is scheduled fortransmission at a given point in time. This estimation is made bymeasuring a baseline reference signal from each UE, such as the DM RS orthe SRS. The baseline reference signal may be a different referencesignal from those used to estimate channel estimation (DM RS) and toestimate the CQI (SRS).

NodeB then allocates 704 a cyclic shift value for to an m-th UE based ona sum of cyclic shifts allocated to previous m-1 UEs of the plurality ofUEs scheduled for uplink transmission during the same transmission timeinterval or sub-frame, where m=[1, total number of UEs scheduled foruplink transmission].

Once all of the UEs in the pool 706 have been allocated a cyclic shiftvalue, then each UE utilizes the allocated cyclic shift to form 708 thetransmitted RS by applying a corresponding cyclic shift to the CAZACsequence, whereby the transmitted RS is orthogonal to each RStransmitted by all others of the plurality of UEs scheduled in the sametime transmission period or sub-frame.

Each UE then transmits 710 the RS in the sub-frame according to thetransmission schedule.

Periodically 712, each UE transmits another baseline RS and theestimation 702 and allocation 704 process is repeated.

FIG. 8 is a block diagram of a UE 1000 with an embodiment adaptivecyclic shift allocation, as described above. Digital system 1000 is arepresentative cell phone that is used by a mobile user. Digitalbaseband (DBB) unit 1002 is a digital processing processor system thatincludes embedded memory and security features. In this embodiment, DBB1002 is an open media access platform (OMAP™) available from TexasInstruments designed for multimedia applications. Some of the processorsin the OMAP family contain a dual-core architecture consisting of both ageneral-purpose host ARM™ (advanced RISC (reduced instruction setprocessor) machine) processor and one or more DSP (digital signalprocessor). The digital signal processor featured is commonly one oranother variant of the Texas Instruments TMS320 series of DSPs. The ARMarchitecture is a 32-bit RISC processor architecture that is widely usedin a number of embedded designs.

Analog baseband (ABB) unit 1004 performs processing on audio datareceived from stereo audio codec (coder/decoder) 1009. Audio codec 1009receives an audio stream from FM Radio tuner 1008 and sends an audiostream to stereo headset 1016 and/or stereo speakers 1018. In otherembodiments, there may be other sources of an audio stream, such acompact disc (CD) player, a solid state memory module, etc. ABB 1004receives a voice data stream from handset microphone 1013 a and sends avoice data stream to handset mono speaker 1013 b. ABB 1004 also receivesa voice data stream from microphone 1014 a and sends a voice data streamto mono headset 1014 b. Usually, ABB and DBB are separate ICs. In mostembodiments, ABB does not embed a programmable processor core, butperforms processing based on configuration of audio paths, filters,gains, etc being setup by software running on the DBB. In an alternateembodiment, ABB processing is performed on the same OMAP processor thatperforms DBB processing. In another embodiment, a separate DSP or othertype of processor performs ABB processing.

RF transceiver 1006 includes a receiver for receiving a stream of codeddata frames from a cellular Node B via antenna 1007 and a transmitterfor transmitting a stream of coded data frames to the cellular Node Bvia antenna 1007. A RS is transmitted to nearby Node Bs andconfiguration commands are received from the serving Node B as describedabove. Transmission of the RS and scheduled resource block transmissionsare configured as described above. In this embodiment, a singletransceiver supports SC-FDMA operation but other embodiments may usemultiple transceivers for different transmission standards. Otherembodiments may have transceivers for a later developed transmissionstandard with appropriate configuration. RF transceiver 1006 isconnected to DBB 1002 which provides processing of the frames of encodeddata being received and transmitted by cell phone 1000.

The basic SC-FDMA DSP radio includes DFT, subcarrier mapping, and IFFTto form a data stream for transmission and DFT, subcarrier de-mappingand IFFT to recover a data stream from a received signal. DFT, IFFT andsubcarrier mapping/de-mapping may be performed by instructions stored inmemory 1012 and executed by DBB 1002 in response to signals received bytransceiver 1006.

DBB unit 1002 may send or receive data to various devices connected toUSB (universal serial bus) port 1026. DBB 1002 is connected to SIM(subscriber identity module) card 1010 and stores and retrievesinformation used for making calls via the cellular system. DBB 1002 isalso connected to memory 1012 that augments the onboard memory and isused for various processing needs. DBB 1002 is connected to Bluetoothbaseband unit 1030 for wireless connection to a microphone 1032 a andheadset 1032 b for sending and receiving voice data.

DBB 1002 is also connected to display 1020 and sends information to itfor interaction with a user of cell phone 1000 during a call process.Display 1020 may also display pictures received from the cellularnetwork, from a local camera 1026, or from other sources such as USB1026.

DBB 1002 may also send a video stream to display 1020 that is receivedfrom various sources such as the cellular network via RF transceiver1006 or camera 1026. DBB 1002 may also send a video stream to anexternal video display unit via encoder 1022 over composite outputterminal 1024. Encoder 1022 provides encoding according toPAL/SECAM/NTSC video standards.

As used herein, the terms “applied,” “connected,” and “connection” meanelectrically connected, including where additional elements may be inthe electrical connection path. “Associated” means a controllingrelationship, such as a memory resource that is controlled by anassociated port. The terms assert, assertion, de-assert, de-assertion,negate and negation are used to avoid confusion when dealing with amixture of active high and active low signals. Assert and assertion areused to indicate that a signal is rendered active, or logically true.De-assert, de-assertion, negate, and negation are used to indicate thata signal is rendered inactive, or logically false.

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the invention will beapparent to persons skilled in the art upon reference to thisdescription. This invention applies to all scheduled communicationsystems which perform channel sounding across multiple resource blocks.This invention applies in uplink and downlink. Embodiments of thisinvention are applicable, but not restricted to, frequency divisionmultiplexed (FDM) reference signal transmission for simultaneoustransmission from multiple UEs. This includes, but is not restricted to,OFDMA, OFDM, FDMA, DFT-spread OFDM, DFT-spread OFDMA, single-carrierOFDMA (SC-OFDMA), and single-carrier OFDM (SC-OFDM) pilot transmission.The enumerated versions of FDM transmission strategies are not mutuallyexclusive, since, for example, single-carrier FDMA (SC-FDMA) may berealized using the Discrete Fourier Transform (DFT)-spread OFDMtechnique. In addition, embodiments of the invention also apply togeneral single-carrier systems.

A Node B is generally a fixed station and may also be called a basetransceiver system (BTS), an access point, or some other terminology. AUE, also commonly referred to as terminal or mobile station, may befixed or mobile and may be a wireless device, a cellular phone, apersonal digital assistant (PDA), a wireless modem card, and so on.

In another embodiment, the cyclic shift allocated to each m-th UE isequal to the sum of a delay spread and a timing uncertainty of each ofthe previous m-1 UEs plus the delay spread of the m-th UE. The term“delay spread” alone also implies inclusion of timing uncertainties.Multiple antennas of the same UE can be treated as another separate UE,except that delay-spread estimation can be common for all antennas ofone UE.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

What is claimed is:
 1. A method for defining transmission parameters ofuser equipment (UE) reference signals (RS), comprising: estimatingchannel delay spreads of a plurality of UEs scheduled for transmissionat a particular transmission time period or sub-frame in an uplink forcommunication with a NodeB; allocating transmission parameters to eachscheduled UE of the plurality of UEs in accordance to the delay spreadsof the plurality of UEs scheduled for transmission in the particulartime period or sub-frame, wherein the parameters comprises a cyclicshift allocated to each m-th UE equal to the sum of a delay spread and atiming uncertainty of each of the previous m-1 UEs, wherein m is equalor greater than 1; and utilizing at the UE the updated allocated cyclicshift to form a later transmitted RS by applying the updated cyclicshift to the CAZAC sequence.
 2. The method of claim 1 wherein theparameters are cyclic shifts.
 3. The method of claim 1, furthercomprising using the RS for channel and CQI estimation.
 4. The method ofclaim 3, wherein estimating delay spreads further comprises periodicallyreceiving a baseline reference signal from each of the plurality of UEsat the NodeB for use in estimating the delay spread of the correspondingUE, and wherein the baseline reference signal is different than the RS.5. The method of claim 1 further comprising sending cyclic shiftallocations to the plurality of scheduled UEs from the NodeB usingdownlink control signaling.
 6. The method of claim 2, further comprisingdetermining a base cyclic shift value to provide orthogonal RSmultiplexing relative to the UE with the largest delay spread; andwherein the cyclic shift allocated to each m-th UE is an integermultiple of the base cyclic value, wherein m is equal or greater than 1.7. The method of claim 6, wherein different base cyclic values can beselected in different operating communication environments.
 8. A methodto adaptively select a cyclic shift applied to a CAZAC sequence forformation of an orthogonal reference signal (RS) transmitted by a userequipment (UE), comprising: estimating delay spreads of a plurality ofUEs scheduled for transmission at a particular transmission time periodor sub-frame in an uplink for communication with a NodeB; allocating acyclic shift to each scheduled UE of the plurality of UEs in accordanceto the delay spreads of the plurality of UEs scheduled for transmissionin the particular time period or sub-frame, such that two or more of theUEs are allocated different non-zero cyclic shift values; and receivinga plurality of reference signals from the respective plurality of UEs,wherein each RS comprises a CAZAC sequence that is cyclically shifted byan amount allocated to each respective UE of the plurality of UEs,whereby each received RS is orthogonal to each RS transmitted by allothers of the plurality of UEs scheduled in the same time transmissionperiod or sub-frame, wherein the cyclic shift allocated to each m-th UEis equal to the sum of a delay spread and a timing uncertainty of eachof the previous m-t UEs, wherein m is equal or greater than
 1. 9. Themethod of claim 8, wherein estimating delay spreads further comprisesperiodically receiving a baseline reference signal from each of theplurality of UEs at the NodeB for use in estimating the delay spread ofthe corresponding UE.
 10. The method of claim 8, further comprisingusing each RS for channel and CQI estimation.
 11. The method of claim 9,wherein the baseline reference signal is different than the RS.
 12. Themethod of claim 8 further comprising sending cyclic shift allocations tothe plurality of scheduled UEs from the NodeB using downlink controlsignaling.
 13. The method of claim 8, further comprising determining abase cyclic shift value to provide orthogonal RS multiplexing relativeto the UE with the largest delay spread; and wherein the cyclic shiftallocated to each m-th UE is an integer multiple of the base cyclicvalue, wherein m is equal or greater than
 1. 14. The method of claim 13,wherein different base cyclic values can be selected in differentoperating communication environments.
 15. A method to adaptively selecta cyclic shift applied to a CAZAC sequence for formation of anorthogonal reference signal (RS) transmitted by a user equipment (UE),comprising: transmitting a baseline reference signal from the UE to aNodeB that us used to estimate a delay spread during transmission of asub-frame from the UE; receiving at the UE a first allocated cyclicshift in accordance to delay spreads of a plurality of UEs scheduled fortransmission in the particular time period or sub-frame; utilizing atthe UE the allocated cyclic shift to form the transmitted RS by applyingthe cyclic shift to the CAZAC sequence; periodically receiving at the UEan adapted allocated cyclic shift that has a different value in responseto dynamic changes to delay spreads of the plurality of UEs scheduledfor transmission in a later particular time period or sub-frame, whereinthe updated allocated cyclic shift are transmission parameters thatcomprises a cyclic shift allocated to each m-th UE equal to the sum of adelay spread and a timing uncertainty of each of the previous m-t UEs;and utilizing at the UE the updated allocated cyclic shift to form alater transmitted RS by applying the updated cyclic shift to the CAZACsequence, wherein m is equal or greater than
 1. 16. The method of claim15, wherein the RS is used for channel and CQI estimation.
 17. Themethod of claim 15 wherein the allocated cyclic shift is received from aserving NodeB using downlink control signaling.
 18. A user equipment(UE) comprising: transmitter circuitry operable to transmit a baselinereference signal from the UE to a NodeB that is used by the NodeB toestimate a delay spread during transmission of a sub-frame from the UE;receiving circuitry operable to receive a first allocated cyclic shiftin accordance to delay spreads of a plurality of UEs scheduled fortransmission in a particular time period or sub-frame, wherein thecyclic shift are transmission parameters for each scheduled UE of theplurality of UEs allocated to each m-th UE equal to the sum of a delayspread and a timing uncertainty of each of the previous m-1 UEs, whereinm is equal or greater than 1; processing circuitry connected to thetransmitter circuitry and to the receiver circuitry operable to utilizethe allocated cyclic shift to form a reference signal (RS) fortransmission by applying the cyclic shift to a CAZAC sequence; whereinthe receiving circuitry periodically receives an updated allocatedcyclic shift that has a different value in response to dynamic changesto delay spreads of the plurality of UEs scheduled for transmission in alater particular time period or sub-frame; and wherein the processingcircuitry is further operable to utilize the updated allocated cyclicshift to form a later transmitted RS by applying the updated cyclicshift to the CAZAC sequence.
 19. A method to adaptively select a cyclicshift applied to a CAZAC sequence for formation of an orthogonalreference signal (RS) transmitted by a user equipment (UE), comprising:estimating delay spreads of a plurality of UEs scheduled fortransmission at a particular transmission time period or sub-frame in anuplink for communication with a NodeB; allocating a cyclic shift to eachscheduled UE of the plurality of UEs in accordance to the delay spreadsof the plurality of UEs scheduled for transmission in the particulartime period or sub-frame, such that two or more of the UEs are allocateddifferent non-zero cyclic shift values, wherein the cyclic shift aretransmission parameters for each scheduled UE of the plurality of UEsallocated to each m-th UE equal to sum of a delay spread and a timinguncertainty of each of the previous m-1 UEs, wherein m is equal orgreater than 1; and utilizing the allocated cyclic shift to form thetransmitted RS by applying a corresponding cyclic shift to the CAZACsequence, whereby the transmitted RS is orthogonal to each RStransmitted by all others of the plurality of UEs scheduled in the sametransmission time period or sub-frame.
 20. The method of claim 19,wherein estimating delay spreads further comprises periodicallytransmitting a baseline reference signal from each of the plurality ofUEs to the NodeB for use in estimating the delay spread of thecorresponding UE.